The present invention relates to a vibration motor, mounted to a communication device, for alerting a user to a message arrival with mechanical vibrations, and the portable communication device using the motor. More particularly, the present invention relates to a motor having an eccentric weight in order to generate greater vibrations. The eccentric weight is accommodated in the motor housing for safety reasons, and yet the motor is small in size.
A driving shaft of a motor is coupled to an eccentric weight, and the motor is spin for rotating the weight, thereby generating desired vibrations. This is a principle of a vibration motor used in a portable communication device such as a pager. However, a fan-shaped or semicircle eccentric weight has been exposed during the rotation, and this has caused some danger. Recently, it is thus proposed that the eccentric weight be housed in the motor case. For instance, Japanese Utility Model Application Non-Examined Publication No. H06-52363 discloses one of the proposed vibration motors.
On the other hand, a part of a rotor is eliminated so that unbalance is produced in the vibration motor. This method can save the eccentric weight, and lower the cost. For instance, Japanese Patent Application Non-Examined Publication No. H06-284662 discloses that a magnet of a rotor of a brush-less motor is cut away by a range of 90xc2x0-180xc2x0 thereby eliminating the eccentric weight. As such, saving the weight seems advantageous to a cost reduction purpose.
Recently, however, the portable communication devices, typically represented by a cellular phone, have been drastically downsized as well as light-weighted. The vibration motor thus should be minimized in size while it keeps a given level of vibrations. The motor with a cut-away magnet discussed above thus must use a substantially large magnet to obtain a required level of vibrations because the specific gravity of the magnet is no more than five (5). The dimensions of this motor include the space of this magnet, therefore, downsizing of this motor comes to a deadlock sooner or later.
The present invention addresses the problems discussed above, and aims to provide a vibration motor that generates large vibrations using an eccentric weight. The weight is accommodated in a motor housing for safety reasons, and yet the motor is small in size.
The vibration motor of the present invention comprises the following elements:
a stator; and
a rotor facing the stator,
in the rotor, magnet and an eccentric weight, of which specific gravity is greater than that of the magnet, are disposed such that a rotational area of the magnet overlaps at least with a part of a rotational area of the eccentric weight.
This structure allows the eccentric weight and the magnet to share a part of their rotational areas. In other words, the magnet is placed in the rotational area of the weight except the area occupied by the weight, so that an entire space of the motor wastes less space. Thus the space can be used in a high density, thereby realizing a thin and compact motor as well as providing the motor generating large vibrations. The rotational area means a space occupied by an object rotating on a center axis.
Another vibration motor of the present invention comprises the following elements:
a stator having a stator core; and
a rotor including cylindrical magnet and an eccentric weight of which specific gravity is greater than that of the magnet,
where the stator core faces the magnet in the radial direction, and a magnetic center of the magnet differs in an axial direction from a magnetic center of the stator core. Also, at least a part of the eccentric weight is placed at a cut-away section of the magnet.
This deviation of the magnetic center of the magnet from that of the stator core in the axial direction allows the magnet to be attracted toward the stator core, i.e., producing magnetic thrust. This magnetic thrust prevents the rotor from coming off the bearing fixed to the stator, and also allows the rotor to rotate in a stable manner with being journaled by the bearing. This structure can be expressed that a part of the magnet is replaced with the eccentric weight, and the replaced magnet section contributes to torque production of the motor, yet its contribution factor is small. Therefore, partial cut-away of the magnet just slightly lowers characteristics of the motor. The thin and compact motor generating large vibrations can be thus obtained.
A device of the present invention comprises the following elements:
a motor;
a board on which the motor is mounted;
a driver for driving the motor,
where the motor comprises the elements respectively discussed above.
These structures allow the device of the present invention to be thin and compact as well as to generate and deliver large vibrations to a user.